The invention relates to data recording on an optical information carrier, and more particularly to a system and method of writing marks corresponding to recording data on a recording surface.
Information is recorded onto a recordable optical information carrier such as a DVD-R (DVD-recordable) or a DVD-RW (DVD-rewritable) by projecting a laser beam onto the recording surface. At the contact areas, the properties of the optical recording medium are physically changed by increased temperature. This generates recording marks on the recording surface.
The laser beam is modulated by recording pulses having time widths corresponding to information to be recorded, such that laser pulses having lengths corresponding to information to be recorded are generated and projected onto the optical information carrier.
Often, a series of pulses comprising a plurality of short pulses, rather than a single laser pulse is used. An employed “write strategy” introduces less heat accumulation on the recording surface compared to the conventional method, such that uniform temperature distribution can be achieved on the recording surface on which the recording marks are formed. This can prevent undesired teardrop-shaped recording marks enabling formation of recording marks of preferred shape.
In the case of DVD-RW, for example, each mark representing data is written by a sequence of one or more pulses, the last of which descends from a write power level to a cooling power level, which sustains for a cooling period before it ascends to an erasing power level. Marks are written by the pulses at the write power level. Erasure of previous marks in the spaces between presently written marks is accomplished by irradiation at the erasing power level. The cooling period following the last pulse of the sequence and preceding the start of the erasure cools the recording surface at the end of the sequence. The duration of the cooling period is a key point in the write strategy, enabling formation of recording marks of preferred shape and length. If the cooling period is too short, erasure starts too soon and erases too much of the just written mark. If, on the other hand, the cooling period is too long, the erasure starts too late and previously written marks immediately following recently written marks will not be erased. Optimum cooling period is influenced by many factors, such as write speed and physical characteristics of the recording surface and the optical information carrier, creating great differences in write strategy when recording marks on different recording surfaces under different conditions.
A conventional technique for obtaining an optimum write strategy is to provide a disc having information on the recording power and the write strategy reflecting characteristics thereof.